A New Ornithischian Dinosaur and the Terrestrial Vertebrate Fauna from a Bone Bed in the Wealden of Ardingly, West Sussex

Maidment et al. in press. Proceedings of the Geologists’ Association A new ornithischian dinosaur and the terrestrial vertebrate fauna from a bone bed in the Wealden of Ardingly, West Sussex Susannah C. R. Maidment1,2*, Chloe Kirkpatrick1, Brian Craik-Smith3,4 & Jane E. Blythe3 1Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, United Kingdom. 2Current address: School of Environment and Technology, University of Brighton, Lewes Road, Brighton, BN2 4GJ. 3Science Department, Ardingly College, College Lane, Ardingly, nr Haywards Heath, West Sussex, RH17 6SQ, United Kingdom. 4Current address: Pinecroft, Flower Farm Close, Henfield, West Sussex, BN5 9 QA, United Kingdom. *Corresponding author: [email protected] Abstract The Wealden Supergroup of south-east England has long been of interest to palaeontologists because of its diverse flora and fauna. The Supergroup is Early Cretaceous in age, occupying the time period immediately after the enigmatic end-Jurassic extinction. Wealden faunas therefore have the potential to be informative about the tempo and mode of post-extinction recovery, but due to lack of exposure in this densely populated part of southern England, are difficult to sample. In the summer of 2012, a number of ex situ fossiliferous blocks of sandstone, siltstone and limestone were discovered from building excavations at Ardingly College, near Haywards Heath in West Sussex. The sedimentology of the blocks indicates that they are from the Valanginian Maidment et al. in press. Proceedings of the Geologists’ Association Hastings Group, and that Ardingly College is underlain by the Grinstead Clay Formation, rather than the Ardingly Sandstone Member. The blocks contain a diverse invertebrate fauna and flora, as well as vertebrate remains, which are found in a distinct sandstone horizon that probably represents the Top Lower Tunbridge Wells pebble bed. A tooth from an ornithschian dinosaur cannot be referred to any of the ornithischian taxa known from the Wealden Supergroup, and therefore represents a new taxon. Teeth of the crocodilian Theriosuchus extend the known range of this taxon in the Wealden, while teeth of an ornithocheird pterosaur confirm the presence of these animals in the skies above the Wealden sub-basins. Fusainized plant remains and the wing-case of a cupedid beatle indicate that wildfire was a ubiquitous feature of the Weald Sub-basin during the Valanginian. Introduction The Wealden Supergroup of the Weald Sub-basin of south-east England comprises a succession of alluvial, lacustrine and lagoonal facies deposited during the Early Cretaceous (Radley & Allen 2012). Documentation of the rocks and their fossils, mainly exposed in small, hand-worked quarries and on sea cliffs, began in the early part of the nineteenth century and continues to this day (Batten 2011). The historical significance of the Wealden strata to vertebrate palaeontologists cannot be overstated: some of the earliest recognised dinosaur remains from anywhere in the world were discovered here (Mantell 1825), and several bone beds within the Wealden succession are well-known (Allen 1949; Cook 1995). Lower Cretaceous faunas are significant because they appear soon after an enigmatic and poorly understood extinction event at the end of the Jurassic Period (e.g. Bambach 2006; Benson et al. 2010; Mannion et al. 2011; Upchurch et al. 2011; Lloyd 2012). Documentation of faunas of this age is therefore important to aid our understanding of the tempo, mode and mechanisms behind this purported extinction and the post-extinction recovery. Unfortunately, vertebrate faunas from the basalmost Cretaceous are poorly known worldwide: the Paleobiology Database (www.paleobiodb.org) lists just 380 collections worldwide for vertebrates Maidment et al. in press. Proceedings of the Geologists’ Association from the Berriasian, and only 197 collections for the Valanginian.). The Hastings Beds Group, dating from the uppermost Berriasian to the Valanginian (Fig. 1; Batten & Austen 2011), is ideally placed stratigraphically to be a case study for this time period. However, many of the small stone quarries and brick pits that littered the landscape of the Weald in the 19th and early 20th centuries, from which dinosaur fossils were discovered, have closed and are overgrown, and opportunities to investigate the rocks and their fossil contents are therefore increasingly scarce. In 2012, a number of ex situ fossiliferous sandstone blocks were collected from a spoil heap formed by excavations for a new building at Ardingly College, West Sussex (Fig. 1), by one of us (B.C.- S.). Examination of the blocks revealed the presence of large bone fragments, teeth and invertebrate remains. Subsequently, we set up a citizen science project involving students of Ardingly College and the local community to search the spoil heaps for more fossiliferous blocks on a number of ‘dino dig days’. Herein, we describe the terrestrial vertebrate fauna discovered at Ardingly College, locate it stratigraphically, and discuss its implications for our understanding of Wealden faunas. All fossiliferous material is accessioned into the collections of the Science Department at Ardingly College. A note on stratigraphic terminology Terminology applied to the strata of the Wealden of the Weald Sub-basin has a complex history. The most commonly-used terminology, and that employed in recent publications such as Batten (2011) and Radley & Allen (2012), considers the Wealden to be a Supergroup, divided into the Hastings Beds Group and the Weald Clay Group, and that terminology is employed here (Fig. 1). It should be noted, however, that this differs from the scheme employed by the British Geological Survey (BGS; Hopson et al. 2008), who consider the Wealden a Group, and do not recognise the Hastings Beds Group. Maidment et al. in press. Proceedings of the Geologists’ Association Institutional abbreviations ARD, Ardingly College, Ardingly, West Sussex, U.K.; NHMUK, The Natural History Museum, London, U.K. Methods The sedimentology of the fossiliferous blocks was examined using traditional petrographic techniques; the fossils were examined using reflected light microscopy. Due to the wooded and residential nature of much of the Weald Sub-basin, few exposures are present. Subsurface sedimentological data in the area was obtained from borehole and trial pit logs drilled by Southern Testing Ltd, from freely available borehole data from the British Geological Survey (BGS; http://mapapps.bgs.ac.uk/geologyofbritain/home.html?mode=boreholes), from the BGS geological map of the area (Horsham Sheet, number 302; Gallois et al. 1972), and from descriptions of logged sections in quarries that are currently inaccessible in Radley & Allen (2012). These data were supplemented by field studies of exposures of the Ardingly Sandstone Member at Balcombe Lane, Ardingly (TQ 33530 29795) and Wakehurst Place (TQ 33636 31761), and of the Grinstead Clay Formation at Rocky Lane, Haywards Heath (TQ 32392 22268; Fig. 2). The latter was a road cutting exposed during building work, affording a rare opportunity to investigate the softer, rarely exposed Grinstead Clay Formation. Sedimentology and stratigraphy Sedimentological analysis of the fossiliferous blocks revealed that they could be divided into five broad lithologies, each with a distinct suite of fossils, indicating that more than one fossiliferous horizon was quarried at the Ardingly site. The five lithologies are: (1) fine-grained quartz arenite with Maidment et al. in press. Proceedings of the Geologists’ Association some iron-rich cement; (2) fine-grained quartz arenite with significant iron-rich cement; (3) bioclastic limestone; (4) micritic limestone; and (5) finely laminated sandstone. Vertebrate remains are restricted to lithologies (1), (2) and (3). Organic remains generally show a preferred alignment. Lithologies (1) and (2) comprise >95% sub-rounded, well-sorted quartz grains, with <5% plagioclase and muscovite. Hand specimens of lithology (2) are black to dark orange, witha pitted surface. The pits are 1-4mm wide and appear to be voids where organic material has been dissolved and/or preferentially weathered, or where clasts have been washed out. Thin-section petrography reveals an irregular, patchy red-brown to opaque cement. Shell moulds are present as voids, and are orientated with bedding. Nodules of an iron compound, 6-20 mm in diameter, are also present. Lithology (1) yields the freshwater bivalve Unio and the freshwater gastropod Viviparus, both preserved in monospecific assemblages. Indeterminate actinopterygian vertebrae are also present. Lithology (2) yields the vertebrate remains described below, teeth and scales of the lepisosteiform fish Scheenstia (formerly Lepidotes; Lopéz-Arbarello 2012;e.g. Fig. 3A; ARDB1; ARDB8A), teeth of the pycnodont fish Ocloedus (formerly Coelodus; Poyato-Ariza & Wenz 2002; ARDB1), and hybodont shark teeth (ARDB4A). Lithology (3) contains a monospecific assemblage of the bivalve Neomiodon, as well as the crocodylian teeth described below. Lithology (4) contains Neomiodon, and the fusainized wing case of a cupedid beetle (Fig. 3B; ARDL9), and numerous fusainized plant remains, including the ferns Phlebopteris (Fig. 3C; ARDL6B) and Gleichenites (ARDL13; ARDL14). Lithology (5) contained fusainized remains of the fern Weichselia (ARDL6A). Several hand specimens preserve more than one of the lithologies described above along with way-up structures, allowing the

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